You can't get more than 45K on plugs despite what Ford claims. It is a myth.
I've seen quite a bit of anecdotal evidence that the 3.5 eats plugs, but I've never seen any claims regarding that on the 5.4. My original plugs got changed at 95K and the second set around 180K. Motorcraft platinum plugs both times. No indication in either case that the plugs were overdue. 45K on the 5.4 seems like throwing money away unless you're using some seriously ****** plugs.
I change everything. COPs, boots, plugs.
I like preventing problems vs waiting for something to fail.
I am now driving 500-1000 miles week. Just got home today and since yesterday till now I clocked 650. I’ve gone through 3 1/2 tank fills this week.
My truck never had a misfire.
Now I’m thinking of replacing the alternator it has over 100k miles.
It's your money to spend however you please, but the COPs and boots are either good or they're not. I know replacing the COPs like they're a maintenance item is a thing for the Expedition crowd, but they virtually never fail if plugs are replaced in a timely fashion. And the boots, well it's easy enough to inspect them now and then just like you would any other rubber hose, etc. If they're starting to look suspect, by all means replace them, but doing it when they're still in great shape doesn't achieve anything.
And the alternator at 100K? Just like that? Why not test it? And why at 100K? I have literally never had an alternator fail before 200K, but if I was going to replace it "just because" as part of some sort of bizarre maintenance routine, 100K seems way, way too early nonetheless.